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Derivative instruments (Details) (USD $) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2013 | Mar. 31, 2013 | Dec. 31, 2012
Derivative instruments [Line Items] |  |  |
Amount of unrealized gain (loss) on hedge at de-designation date to be reclassified into AOCI |  | $ 1,800,000 |
Amount of time remaining to transfer accumulated other comprehensive income to earnings | 12 months |  |
Cash flow hedge gain (loss) to be reclassified within twelve months | (700,000) |  |
Derivatives with credit-risk-related contingent feature in net liability position, aggregate fair value | 7,500,000 |  | 6,300,000
Assets needed for immediate settlement aggregate fair value for cash flow heding instruments | 7,500,000 |  | 6,300,000
Oil swap and or collar [Member] |  |  |
Derivative instruments [Line Items] |  |  |
Derivative, nonmonetary notional amount | 2,900,000 |  | 2,600,000
Natural gas swap or and collar [Member] |  |  |
Derivative instruments [Line Items] |  |  |
Derivative, nonmonetary notional amount | 18,300,000 |  | 11,000,000
Interest rate derivative instruments |  |  |
Derivative instruments [Line Items] |  |  |
Notional amount of interest rate cash flow hedge derivatives |  |  | $ 50,000,000

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- Definition Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Amount of unrealized gain (loss) on hedge at de-designation date to be reclassified into accumulated other comprehensive income over time. + References No definition available. + Details
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- Definition The aggregate fair value of assets needed to immediately settle the derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624258-113959 + Details
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- Definition The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=7668309&loc=d3e80748-113994 + Details
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- Definition Estimated period for the anticipated transfer of gain (loss), net, from accumulated other comprehensive income into earnings, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Details
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- Definition The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624258-113959 + Details
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